MIDI and Hardware¶

krach connects to external MIDI controllers and audio hardware for hands-on control of your live coding session.

MIDI CC mapping¶

Map a MIDI continuous controller to any voice or bus parameter:

kr.midi_map(cc=74, path="bass/cutoff", lo=200.0, hi=4000.0)

The CC value (0--127) is scaled linearly to the lo--hi range and applied to the parameter in real time.

Parameters¶

Parameter	Description
`cc`	MIDI CC number (0--127)
`path`	Control path, e.g. `"bass/cutoff"`, `"verb/room"`
`lo`	Value when CC is 0
`hi`	Value when CC is 127
`channel`	MIDI channel (optional, defaults to all channels)

Examples¶

# Knob 74 controls bass filter cutoff
kr.midi_map(cc=74, path="bass/cutoff", lo=200.0, hi=4000.0)

# Knob 1 (mod wheel) controls bass gain, channel 5 only
kr.midi_map(cc=1, path="bass/gain", lo=0.0, hi=1.0, channel=5)

# Map reverb room size to a fader
kr.midi_map(cc=7, path="verb/room", lo=0.0, hi=1.0)

# Master volume on a fader
kr.midi_map(cc=7, path="master", lo=0.0, hi=1.0, channel=1)

Typical controller mappings¶

A practical starting point for an 8-knob MIDI controller:

kr.midi_map(cc=70, path="kick/gain", lo=0.0, hi=1.0)
kr.midi_map(cc=71, path="hat/gain", lo=0.0, hi=1.0)
kr.midi_map(cc=72, path="bass/gain", lo=0.0, hi=1.0)
kr.midi_map(cc=73, path="lead/gain", lo=0.0, hi=1.0)
kr.midi_map(cc=74, path="bass/cutoff", lo=200.0, hi=4000.0)
kr.midi_map(cc=75, path="lead/cutoff", lo=500.0, hi=8000.0)
kr.midi_map(cc=76, path="verb/room", lo=0.0, hi=1.0)
kr.midi_map(cc=77, path="verb/gain", lo=0.0, hi=0.8)

ADC input: live audio¶

Capture audio from your system's audio interface (CoreAudio on macOS):

mic = kr.input("mic", channel=0, gain=0.5)

Parameters¶

Parameter	Description
`name`	Label for the input (e.g. `"mic"`, `"guitar"`)
`channel`	ADC input channel (0-indexed)
`gain`	Input gain (0.0--1.0)

Routing input to effects¶

Live audio inputs can be sent to buses just like voices:

mic = kr.input("mic", channel=0, gain=0.5)
verb = kr.node("verb", reverb_fn, gain=0.3)

mic.send(verb, 0.4)   # send mic to reverb at 40%

Multiple inputs¶

mic = kr.input("mic", channel=0, gain=0.5)
guitar = kr.input("guitar", channel=1, gain=0.7)

mic.send(verb, 0.3)
guitar.send(verb, 0.5)

MIDI clock output¶

krach can send MIDI clock to sync external hardware (drum machines, sequencers, synths). Enable it with an environment variable before starting the REPL:

KRACH_MIDI_CLOCK=1 ./bin/krach

The clock follows kr.tempo and sends standard MIDI clock messages (24 ppqn) to all connected MIDI outputs.

Hardware setup tips¶

Audio interface -- krach uses CoreAudio on macOS. Set your preferred interface in Audio MIDI Setup before starting the REPL. Lower buffer sizes give lower latency but higher CPU load.

MIDI controllers -- any class-compliant USB MIDI controller works. No driver installation needed on macOS. Plug in before starting the REPL.

Channel isolation -- use the channel= parameter on kr.midi_map() when multiple controllers are connected, to avoid CC collisions.

Persisting mappings -- save your MIDI mappings in a setup script and load it at the start of each session:

# midi_setup.py
kr.midi_map(cc=74, path="bass/cutoff", lo=200.0, hi=4000.0)
kr.midi_map(cc=1, path="bass/gain", lo=0.0, hi=1.0)
kr.midi_map(cc=7, path="verb/room", lo=0.0, hi=1.0)

# In the REPL
kr.load("midi_setup.py")

Monitoring latency -- for live performance with external audio input, keep your audio buffer size at 128 or 256 samples. At 44.1 kHz, 128 samples is about 3 ms of latency.